1. Field of the Invention
The present invention relates to the field of door latches, locks and deadbolts.
2. Prior Art
A normal door latch cooperates with a simple striker plate, to be cammed thereby to a latch withdrawn position against a spring encouraging the latch to an extended position, with the latch moving under the spring force to the extended position when the latch aligns with the opening in the striker plate at the door closed position. Without more, the latch may be cammed to the latch withdrawn position and the door opened by using a thin card or knife to reach between the door jamb and the door to withdraw the latch. This type of unwanted latch withdrawal is prevented in some locks by a sensing pin adjacent the latch which will cam with the latch on closing the door, though will intercept the striker plate and not extend when the latch springs into the opening in the striker plate. The extension of the latch without the corresponding extension of this sensing pin is operative to lock the latch in the extended position, and then make the same retractable only by the inner and outer knob. In either event however, a typical latch bolt will only extend no more than approximately one half inch into the striker plate. In most cases this will allow a would-be intruder to extend a pry bar between the edge of the door and the door jamb to sufficiently spring the combination to force the door open without withdrawing the latch.
To prevent the foregoing type of unauthorized entry, deadbolts are commonly used in addition to latch bolts. Such deadbolts do not cam on door closure, and accordingly must be manually placed in the withdrawn position for the opening and closing of the door, and thereafter manually extended by use of an external key, or on the inside, by a key or a simple manual control. In comparison to latches, deadbolts will extend into the plate on the door jamb much further than a simple latch bolt, such as by way of example, typically extending a full inch or more through the deadbolt plate and into the door jamb. This normally precludes forcible entry, as a typical door of any substantial structure cannot be sprung enough for the deadbolt to be withdrawn from the deadbolt plate.
Recently, the Wiser Lock Company introduced a lock set referred to as the Weiserbolt lock set having the outward appearance of a conventional latch bolt lock set, but which lock set further includes a "built-in security deadbolt". In one mode of operation, namely the unlocked mode, the lock set operates like a conventional latch set, the latch camming in the normal manner upon closure of the door and being retractable to open the door by operation of either the inner or outer door knobs. In the locked condition however, either through the use of a key from the outside or manual control from the inside, the latch bolt is further extended to a typical deadbolt position, and is retained at the extended position so as to not be camable or otherwise withdrawable, except through the use of the outer key lock or by rotation of the inner door knob. Extending the latch bolt to the normal deadbolt position also disengages the outer knob from the normal latch operating mechanism so that forcible rotation of the outer knob cannot withdraw the bolt.
The foregoing type of lock has a number of advantages. It is in general easier to install than lock sets which use a separate latch bolt and deadbolt, as fewer holes are required in both the door and the door jamb, and fewer assemblies must be attached thereto. Further, the foregoing lock is more convenient to use, as the door may be opened from the inside even when the bolt is extended to the deadbolt position by mere rotation of the knob, rather than by operation first of the deadbolt retracting mechanism and then rotation of the knob. It is of course also safer in that in an emergency such as a fire, the door may be opened from the inside, again by mere rotation of the knob, a natural human reaction when confronted with a closed door and requiring no more time than the opening of an unlocked door. The lock has one characteristic however, which is less than ideal, which the present invention overcomes. In particular, the latch can only be extended to the deadbolt position by operation of the manual control from inside the closed door or by use of the key lock from outside the closed door. This means that one leaving the premises without a key cannot use the deadbolt feature, as the latch can only be extended to the deadbolt position from outside by the use of the key. It is to this problem that the present invention is directed. In particular, in accordance with the present invention, the lock set may be set from inside, not to then extend the latch bolt to the deadbolt position, but rather to set the same so that upon closure of the door the latch bolt will first cam on the striker plate to allow the door to close, and then will automatically extend into the striker plate to the deadbolt extended position and lock at that position until withdrawn either through use of a key from the outside, or by rotation of the interior knob. Thus, unlike the present Wiser lock, the present invention will allow use of the deadbolt feature when leaving the premises without requiring the use of a key, a feature more convenient for those who have a key, and of course essential for the use of the deadbolt feature by those who do not have a key, but desire to extend the deadbolt for added security when they leave the premises.
In U.S. Pat. No. 3,353,858 a lock unit with an extendable latch bolt is disclosed. In this design a lock unit is provided with an extendable latch bolt having considerably more than the usual excursion or travel, so that more than the usual amount of latch bolt engages with the strike when the door is closed, but there is no abnormal projection of the latch bolt when the door is opened. However, the latch bolt itself is relatively short so that when fully extended very little of the latch bolt remains within the structure in the casing of the door to be very secure therein. Also, it appears that the latch bolt is extendable on every door closing whether the lock is locked or not, thereby increasing wear within the system and possibly increasing the actuation forces needed by a user when the lock is unlocked, which in most cases is the large majority of operations of the lock system. In U.S. Pat. Nos. 3,872,697 and 3,933,380, lock mechanisms are disclosed which have a bolt which can be automatically projected on closing of a door to an advanced or projected position and locked in such position to effectively serve as a dead bolt. These designs however are entirely different from that of the present invention, which is believed to be of greater simplicity and lower cost, as well as consistent with standard door jamb opening locations for conventional lock sets.
Finally, other mechanisms of similar characteristics are disclosed in U.S. Pat. Nos. 3,891,255, 3,912,309 and 3,930,677.